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Tom Holvoet

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22 papers
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22

AAMAS Conference 2025 Conference Paper

Efficient Model Checking with Semantically-Equivalent Models for vGOAL

  • Yi Yang
  • Tom Holvoet

Model checking offers a powerful approach to ensuring safety and reliability in autonomous systems. However, existing modelchecking approaches for agent programming languages (APLs) face challenges in equivalent semantic mapping, efficient model generation, and integration with high-performance model checkers. We present a computation tree logic (CTL) model-checking framework for vGOAL, where both the interpreter and model-checking framework share the same state update implementations. Our framework establishes semantically equivalent models of vGOAL programs, implements efficient state space generation, and integrates with the NuSMV model checker. Through a case study of an autonomous logistic system with up to three robots, we demonstrate significant improvements in model-checking efficiency, enabling verification of complex autonomous systems.

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TAAS Journal 2019 Journal Article

UAVs vs. Pirates

  • Ruiwen Zhang
  • Tom Holvoet
  • Bifeng Song
  • Yang Pei

For the rising hazard of pirate attacks, unmanned aerial vehicle (UAV) swarm monitoring is a promising countermeasure. Previous monitoring methods have deficiencies in either adaptivity to dynamic events or simple but effective path coordination mechanisms, and they are inapplicable to the large-area, low-target-density, and long-duration persistent counter-piracy monitoring. This article proposes a self-organized UAV swarm counter-piracy monitoring method. Based on the pheromone map, this method is characterized by (1) a reservation mechanism for anticipatory path coordination and (2) a ship-adaptive mechanism for adapting to merchant ship distributions. A heuristic depth-first branch and bound search algorithm is designed for solving individual path planning. Simulation experiments are conducted to study the optimal number of plan steps and adaptivity scaling factor for different numbers of UAVs. Results show that merely decreasing revisit intervals cannot effectively reduce pirate attacks. Without the ship-adaptive mechanism, the proposed method reduces up to 87.2%, 43.2%, and 5.5% of revisit intervals compared to the Lèvy Walk method, the sweep method, and the baseline self-organized method, respectively, but cannot reduce pirate attacks; while with the ship-adaptive mechanism, the proposed method can reduce pirate attacks by up to 6.7% compared to the best of the baseline methods.

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JAAMAS Journal 2017 Journal Article

When do agents outperform centralized algorithms?

  • Rinde R. S. van Lon
  • Tom Holvoet

Abstract Multi-agent systems (MAS) literature often assumes decentralized MAS to be especially suited for dynamic and large scale problems. In operational research, however, the prevailing paradigm is the use of centralized algorithms. Present paper empirically evaluates whether a multi-agent system can outperform a centralized algorithm in dynamic and large scale logistics problems. This evaluation is novel in three aspects: (1) to ensure fairness both implementations are subject to the same constraints with respect to hardware resources and software limitations, (2) the implementations are systematically evaluated with varying problem properties, and (3) all code is open source, facilitating reproduction and extension of the experiments. Existing work lacks a systematic evaluation of centralized versus decentralized paradigms due to the absence of a real-time logistics simulator with support for both paradigms and a dataset of problem instances with varying properties. We extended an existing logistics simulator to be able to perform real-time experiments and we use a recent dataset of dynamic pickup-and-delivery problem with time windows instances with varying levels of dynamism, urgency, and scale. The OptaPlanner constraint satisfaction solver is used in a centralized way to compute a global schedule and used as part of a decentralized MAS based on the dynamic contract-net protocol (DynCNET) algorithm. The experiments show that the DynCNET MAS finds solutions with a relatively lower operating cost when a problem has all following three properties: medium to high dynamism, high urgency, and medium to large scale. In these circumstances, the centralized algorithm finds solutions with an average cost of 112. 3% of the solutions found by the MAS. However, averaged over all scenario types, the average cost of the centralized algorithm is 94. 2%. The results indicate that the MAS performs best on very urgent problems that are medium to large scale.

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TAAS Journal 2015 Journal Article

SASO 2013

  • Jeremy Pitt
  • Tom Holvoet

IEEE SASO (Self-Adapting and Self-Organizing Systems) is the premier international conference for computer systems and networks that autonomously change some aspect of themselves: code, form, function, shape, structure, components, and so on. Over the past 10 years, it has emerged as a key multidisciplinary event for sharing theoretical insights and technical innovations across the numerous scientific fields and application domains impacted by this research. In 2013, the conference was hosted by Drexel University in Philadelphia, Pennsylvania, and offered an extensive program of high-quality papers. This special issue of ACM TAAS presents selected, revised, and extended best articles, which showcase the rich variety and depth of the SASO scientific community.

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EAAI Journal 2014 Journal Article

ATALK: A decentralized agent platform for engineering open and dynamic organizations

  • Ning Gui
  • Vincenzo De Florio
  • Tom Holvoet

In recent years the concept of “organization” has been gradually accepted as a suitable abstraction for the development of open multi-agent systems with dynamic agents. By modelling interactions based on roles, this abstraction allows an organization to be modelled independently of its participating agents so as to support agent dynamicity. A natural requirement from the abstraction is that agents need to be “organization aware”—that is they must be able to inquire, import, and execute roles from the organization. However, how to adequately support those processes in a decentralized and dynamic environment is still an open issue. This paper addresses this problem by presenting ATALK, a novel decentralized agent middleware that fulfills the above requirements. A role component model is designed to facilitate role deployment, reflection and uniform role interaction. In order to support role dynamicity, a compositional agent architecture allowing dynamic role integration and enactment is proposed. Moreover, ATALK allows agents to hand over their role to other agents of a same organization with their run-time states. Thus, agents can dynamically relinquish their roles without jeopardizing the normal execution of the organization. This paper also evaluates our design and current prototypic implementation through both qualitative analysis and simulations. Our results show that ATALK achieves remarkable organization reconfigurability with little additional overhead.

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IS Journal 2014 Journal Article

Traffic Coordination Using Aggregation-Based Traffic Predictions

  • Rutger Claes
  • Tom Holvoet

A route-guidance system is described, which aggregates information obtained from the drivers participating in the system. Because the data is information related to the future state of the traffic network, the system doesn't require extrapolation from the current traffic network to make predictions about the future state of the traffic network.

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AAMAS Conference 2011 Conference Paper

Decentralized Coordination Of Plug-in Hybrid Vehicles For Imbalance Reduction In A Smart Grid

  • Stijn Vandael
  • Klaas De Craemer
  • Nelis Bouck
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  • Tom Holvoet
  • Geert Deconinck

Intelligent electricity grids, or `Smart Grids', are being introduced at a rapid pace. Smart grids allow the management of new distributed power generators such as solar panels and wind turbines, and innovative power consumers such as plug-in hybrid vehicles. One challenge in Smart Grids is to fulfill consumer demands while avoiding infrastructure overloads. Another challenge is to reduce imbalance costs: after ahead scheduling of production and consumption (the so-called `load schedule'), unpredictable changes in production and consumption yield a cost for repairing this balance. To cope with these risks and costs, we propose a decentralized, multi-agent system solution for coordinated charging of PHEVs in a Smart Grid. Essentially, the MAS utilizes an "intention graph" for expressing the flexibility of a fleet of PHEVs. Based on this flexibility, charging of PHEVs can be rescheduled in real-time to reduce imbalances. We discuss and evaluate two scheduling strategies for reducing imbalance costs: reactive scheduling and proactive scheduling. Simulations show that reactive scheduling is able to reduce imbalance costs by 14%, while proactive scheduling yields the highest imbalance cost reduction of 44%.

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AAMAS Conference 2010 Conference Paper

MAS-DisCoSim 4 PDP: A Testbed for Multi-Agent Solutions to PDPs

  • Jelle Van Gompel
  • Bart Tuts
  • Rutger Claes
  • Mario Cruz Torres
  • Tom Holvoet

This demo illustrates MAS-DisCoSim 4 PDP, a testbed environment for evaluating distributed multi-agent system solutions to pickup and delivery problems (PDPs). PDPs arewell-studied problems in operational research, and providea quite suitable context for testing and evaluating a widevariety of distributed solutions, using particular reasoningand/or coordination mechanisms. The testbed provides areusable simulation framework, and a particular model forPDP environments. The demo illustrates the testbed by showing two MAS-based solutions, one based on gradient field coordination, asecond solution based on the coordination mechanism called'delegate MAS'. The demo is interactive: a user can selectany part of a map, downloaded from the OpenStreetMapwebsite, can run various experiments, and can change - during simulation - various problem and solution characteristicsand observe their effct.

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TAAS Journal 2010 Journal Article

The MACODO middleware for context-driven dynamic agent organizations

  • Danny Weyns
  • Robrecht Haesevoets
  • Alexander Helleboogh
  • Tom Holvoet
  • Wouter Joosen

One of the major challenges in engineering distributed multiagent systems is the coordination necessary to align the behavior of different agents. Decentralization of control implies a style of coordination in which the agents cooperate as peers with respect to each other and no agent has global control over the system, or global knowledge about the system. The dynamic interactions and collaborations among agents are usually structured and managed by means of roles and organizations. In existing approaches agents typically have a dual responsibility: on the one hand playing roles within the organization, on the other hand managing the life-cycle of the organization itself, for example, setting up the organization and managing organization dynamics. Engineering realistic multiagent systems in which agents encapsulate this dual responsibility is a complex task. In this article, we present a middleware for context-driven dynamic agent organizations. The middleware is part of an integrated approach, called MACODO: Middleware Architecture for COntext-driven Dynamic agent Organizations. The complementary part of the MACODO approach is an organization model that defines abstractions to support application developers in describing dynamic organizations, as described in Weyns et al. [2010]. The MACODO middleware offers the life-cycle management of dynamic organizations as a reusable service separated from the agents, which makes it easier to understand, design, and manage dynamic organizations in multiagent systems. We give a detailed description of the software architecture of the MADOCO middleware. The software architecture describes the essential building blocks of a distributed middleware platform that supports the MACODO organization model. We used the middleware architecture to develop a prototype middleware platform for a traffic monitoring application. We evaluate the MACODO middeware architecture by assessing the adaptability, scalability, and robustness of the prototype platform.

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JAAMAS Journal 2008 Journal Article

A field-based versus a protocol-based approach for adaptive task assignment

  • Danny Weyns
  • Nelis Boucké
  • Tom Holvoet

Abstract Task assignment in multi-agent systems is a complex coordination problem, in particular in systems that are subject to dynamic and changing operating conditions. To enable agents to deal with dynamism and change, adaptive task assignment approaches are needed. In this paper, we study two approaches for adaptive task assignment that are characteristic for two classical families of task assignment approaches. FiTA is a field-based approach in which tasks emit fields in the environment that guide idle agents to tasks. DynCNET is a protocol-based approach that extends Standard Contract Net (CNET). In DynCNET, agents use explicit negotiation to assign tasks. We compare both approaches in a simulation of an industrial automated transportation system. Our experiences show that: (1) the performance of DynCNET and FiTA are similar, while both outperform CNET; (2) the complexity to engineer DynCNET is similar to FiTA but much more complex than CNET; (3) whereas task assignment with FiTA is an emergent solution, DynCNET specifies the interaction among agents explicitly allowing engineers to reason on the assignment of tasks, (4) FiTA is inherently robust to message loss while DynCNET requires substantial additional support. The tradeoff between (3) and (4) is an important criteria for the selection of an adaptive task assignment approach in practice.

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EUMAS Conference 2006 Conference Paper

DynCNET: A Protocol for Flexible Task Assignment Applied in an AGV Transportation System

  • Danny Weyns
  • Nelis Boucké
  • Tom Holvoet
  • Kurt Schelfthout

The work presented in this paper is part of an ongoing effort to study suitable task assignment mechanisms for decentralized MAS. Our focus is on systems that are characterized by tasks with delayed commencement. Such a task requires a preceding effort before the agent can start executing the task. An example is a robot that first has to move to the location of a task before it can start executing that task. Important quality requirements for assigning tasks with delayed commencement are flexibility (enable agents to adapt task assignment with changing circumstances) and openness (enable agents to take into account other agents that come and go during the process of task assignment). In previous work, we have studied Contract Net (CNET) and a field-based approach for task assignment (FiTA). CNET does not provide the required flexibility and openness. FiTA satisfies the required qualities, however, the field-based approach provides an emergent solution for task assignment. It is well known that emergent solutions are difficult to engineer and reason about. This raises the question whether it is not easier to extend CNET to take dynamics and changes into account. This paper presents the DynCNET protocol. DynCNET is an extention of CNET, with “Dyn” referring to support for dynamic task assignment. DynCNET provides flexibility and openness for assigning tasks with delayed commencement. We compare the DynCNET protocol with CNET and FiTA in an AGV transportation system. Our experiences in this real-world setting show that: (1) the performance of DynCNET and FiTA are similar, while both outperform CNET; (2) extending CNET to deal with delayed commencement of tasks is not obvious; the complexity to engineer DynCNET is similar to FiTA but much more complex than CNET; (3) whereas task assignment with FiTA is an emergent solution, DynCNET explicitly specifies the interaction among agents allowing engineers to reason on the assignment of tasks. This latter property may be of overriding importance in the selection of an agent-based approach for task assignment in practice.

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EUMAS Conference 2006 Conference Paper

Exploiting the Environment for Coordinating Agent Intentions

  • Tom Holvoet
  • Paul Valckenaers

One interesting family of MAS applications is characterized (1) by their large scale in terms of number of agents and physical distribution, (2) by their very dynamic nature and (3) by their complex functional and non-functional requirements. This family includes a. o. manufacturing control, traffic control and web service coordination. For this family, the complexity of the software for the individual agents using traditional BDI-approaches is overwhelming. In this paper, we present an innovative approach to BDI which alleviates agent complexity through “delegate MASs”, which use the environment and its resources to obtain BDI functionality. Delegate MASs consist of light-weight agents, which are issued either by resources for building and maintaining information on the environment, or by task agents in order to explore the options on behalf of the agents and to coordinate their intentions. We describe the approach, and validate it in a case study of manufacturing control. The evaluation in this case study shows the feasibility of the approach in coping with the large scale of the application and shows that the approach elegantly achieves flexibility in highly dynamic environments. This paper is a two-page discussion introducing a more extensive paper, accepted for publication in the E4MAS 2006 postproceedings.

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JAAMAS Journal 2006 Journal Article

Infrastructures for the environment of multiagent systems

  • Mirko Viroli
  • Tom Holvoet
  • Franco Zambonelli

Abstract The notion of environment is receiving an increasing attention in the development of multiagent applications. This is witnessed by the emergence of a number of infrastructures providing agent designers with useful means to develop the agent environment, and thus to structure an effective multiagent application. In this paper we analyse the role and features of such infrastructures, and survey some relevant examples. We endorse a general viewpoint where the environment of a multiagent system is seen as a set of basic bricks we call environment abstractions, which (i) provide agents with services useful for achieving individual and social goals, and (ii) are supported by some underlying software infrastructure managing their creation and exploitation. Accordingly, we focus the survey on the opportunities that environment infrastructures provide to system designers when developing multiagent applications.

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KER Journal 2005 Journal Article

Environments in multiagent systems

  • Danny Weyns
  • Michael Schumacher
  • Alessandro Ricci
  • Mirko Viroli
  • Tom Holvoet

There is a growing awareness in the multiagent systems research community that the environment plays a prominent role in multiagent systems. Originating from research on behavior-based agent systems and situated multiagent systems, the importance of the environment is now gradually being accepted in the multiagent system community in general. In this paper, we put forward the environment as a first-order abstraction in multiagent systems. This position is motivated by the fact that several aspects of multiagent systems that conceptually do not belong to agents themselves should not be assigned to, or hosted inside the agents. Examples are infrastructure for communication, the topology of a spatial domain or support for the action model. These and other aspects should be considered explicitly. The environment is the natural candidate to encapsulate these aspects. We elaborate on environment engineering, and we illustrate how the environment plays a central role in a real-world multiagent system application.

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